JPS6186162A - Method and device for acoustically detecting contact betweencutting tool and work - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Background of the Invention The present invention is a monitoring device for a machine hoeing machine, and a monitoring device for measuring the vibration of a cutting tool in order to detect the initial contact with the workpiece in order to measure the dimensions of the workpiece online. It relates to a method of sensing.

When machining complex metal parts, such as aircraft engine parts, the dimensions of each part may have to be inspected up to 100 times during the visual machining process.

The time required for this inspection occupies a considerable proportion of the entire machining time, and therefore has a large impact on the productivity of the machining process.

■The flexible method of using the shell itself to measure the dimensions of parts reduces the time devoted to this function and increases productivity. The tool contact sensing device must be very sensitive and very fast because the tool must stop its advancement precisely at the workpiece surface or it may damage the part.

A number of different off-line and on-line methods of measuring the dimensions of parts have been developed or proposed. On-line methods include laser interferometers and retractable touch trigger probes.

■By sensing the vibration of the tool using the shell itself,
U.S. Patent No. 4.4 technology for detecting contact between tool and workpiece
28.055.

The present invention is an improvement over these and other prior art devices that reduces false alarms and provides greater sensitivity.

To detect initial contact between an advancing cutting tool and a workpiece surface before the tool has become used to contaminating the workpiece, tool contact detectors detect very small vibrations generated by light rubbing contact. A signal must be detected. To avoid false alarms, the tool contact sensing device must ignore or reject all other signals. According to field tests,
During a contact test, the amplitude of the signal of a light rubbing contact can be reduced by 10% due to the operation of the lathe, although the noise source of the machine, which normally has low vibrational frequencies, is discriminated in the frequency domain.
It has been found that spike-like noises with amplitudes exceeding 0 times or more are generated. The problem is to immediately detect low amplitude, continuous light rubbing contact signals while rejecting such high amplitude, short duration noise pulses.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tool contact detection system that requires less delay than comparable systems that do not use the cutting tool as a probe, and that is less costly to implement than many competing systems. It is to provide.

Another object is to provide an improved shell contact detector that has adequate sensitivity and is not susceptible to false alarms for most lathe and machine tool equipment.

Another object is to provide a monitoring device that can be easily integrated with an acoustic single tool breakage detector to form a tool breakage and tool contact detection device.

A vibration sensor such as an accelerometer, which is most sensitive to vibration frequencies around the resonance frequency, is placed on the machine tool to sense vibrations at the interface between the tool and the workpiece. An analog pre-processor includes means for high-pass filtering and amplifying the vibration signal to discriminate mechanical noise with lower vibration frequencies, and means for rectifying and low-pass filtering the signal to identify resonance. and means for detecting energy within a band centered on the frequency.

The cutoff frequency of the low-pass filter is lower than 500 Hz to prevent aliasing due to subsequent sampling operations.The unipolar output signal of the analog preprocessor is sampled, The sample is converted to digital form and analyzed by a digital circuit. This digital circuit is programmable and general purpose; it can be a machine. Generated by the operation of the machine tool without contact between the tool and the workpiece. The tool compares every sample with a known amplitude threshold level that is a minimum multiple of successive traverse Xtffi signal levels and detects at least one sample above the amplitude threshold. Means is provided for immediately generating a tool contact alarm signal sent to the control of the machine tool to stop the advance of the tool.

In a preferred embodiment, after a single pull above an amplitude threshold is detected, valid tool contact is confirmed and;
Pattern recognition logic is provided to ignore spike-like noise pulses prior to contact to prevent false alarms. Good tool contact is delayed for a period longer than the maximum known duration of the high amplitude noise pulse. One method is to process each sample for a preset confirmation period.
counting the number of samples above the amplitude threshold or the number of samples below the amplitude threshold. When the number of samples higher than the amplitude measurement reaches a preset number before the end of the verification period, or when counting samples lower than the amplitude equivalent, the number of samples by the end of the verification period reaches the preset number. When the specified number is not reached, a contact alarm will be generated. Another way to use an increment/decrement counter is to operate by ``increasing the count in response to samples above the amplitude threshold and decrementing the count in response to samples below the amplitude threshold, or vice versa''; An alarm is issued when an excess of the scheduled number of samples is detected.

Detailed Description of the Invention ■The location for installing the vibration sensor to detect simple contact is
It is determined individually for each machine tool to be monitored. There is a wide variety of lathes on which this machine tool monitoring system can operate. There are lathes with a horizontal spindle and lathes with a vertical spindle.

The lathes of the above have only one tool holder mounting position, but the Haku lathes have many positions, and in the latter case, several tool holder positions are distributed around the turret, and the turret is rotated. This allows the operator to bring any tool selected by the operator to the cutting position. The lathe may be equipped with auxiliary power equipment such as an automatic tool changer. This monitoring device can also be applied to other types of machine tools such as milling machines, machining centers and drills. 9 Machine tool sensor mounting has a number of sometimes conflicting objectives that must be balanced when selecting and evaluating locations. Examples include, firstly, acoustic coupling of vibration signal bands containing tool contact signal information. These signals are generated at or near the interface between the cutting tool JIII mass and the workpiece. Before it can be detected, it must be propagated to the sensor location.

Attenuation and distortion in the propagation path are a function of the distance and shape of the path, and in particular the number of mechanical interfaces between the signal source and the sensor. Second is the location of the spurious signal source.

The spurious signal source may be close to the desired signal source and reach the sensor via the same or similar path.

However, in any given machine, sources of spurious signals such as hydraulic valves, bearings, and auxiliary equipment are located at other locations that are more or less favorable to the propagation path to a particular sensor mounting location.

It is desirable to mount the sensor where its acoustic coupling to the desired signal source is relatively good and its acoustic coupling to the primary interference or spurious signal source is relatively poor.

Third is the physical protection of the sensor and its cable. The best sensor location from an acoustic coupling standpoint is probably on the tool holder near the cutting edge of the tool insert. However, in this mounting location, the sensor, its cable and cable collector are exposed to an extremely hostile physical environment in terms of force, temperature and cutting fluid contamination. Fourth
The second goal is to minimize the number of sensors and sensor signal processing channels. In machines where several holder mounts have positions, the decision to mount the sensor on the tool holder means that each tool holder mount provides a respective sensor and signal processing channel for the position. This is highly undesirable. Fifth, the available physical space varies widely from machine to machine. The sensor of the present invention, as well as the integrated electronics package, is physically very small, which makes the available mounting locations highly selective.

Figure 1 (Machine frame 10, main shaft 11, chuck 1
2) Jig 13 that holds the workpiece 14 and NO control section 15
1 is a schematic diagram of a portion of a horizontal turret lathe with a A rotatable tool turret 16 has several tool posts 17 supporting tool holders and inserts 18. Turret 16
is supported by a turret stand 19 that moves along two lateral slides 20.

A vibration sensor 21, such as a broadband accelerometer, is mounted on the turret 16. Thus, one sensor in one mounting position can monitor any tool holder position selected by the operator for a cutting operation. This mounting is usually located such that the signal to spurious signal (noise) ratio is satisfactory. Since the turret is rotatable, and in many machines only rotates in one direction, the sensor cannot be electrically connected to stationary signal processing circuitry by a simple cable. Rotary electrical coupling 22 is one method of transmitting electrical signals output from the sensor.

Optionally, a vibration sensor 23 is attached to the transverse slide. In this case, tests have shown that good operation is obtained with the lathe consisting of: Whether the sensor can be mounted away from the turret is something that must be determined experimentally for each machine being monitored.

A vertical turret lathe is shown in FIG. 2, and two suitable mountings of vibration sensors are shown in position. The frame 24 of the IM machine, the tick 25, the workpiece holding jig 26, the workpiece 27, the horizontal slide 28, the vertical slide 29, the rotatable tool turret 30, the tool column 31, and the tool holder and cutting insert 32 is shown (numerical controller not shown).

A vibration signal generated by a sensor 33 mounted on the turret is transmitted via a rotary electrical coupling 34 to a tool contact detection circuit. Another mounting location is on one tool slide of a machine tool. Sensor 35 is vertical slide 29
and is in good acoustic contact.

The main features of the tool contact detection device are shown in FIG.

The C laser 36 is a broadband accelerometer that has a flat response from very low frequencies to just below the resonant frequency, eg, 40 KHz or higher.

This resonance is lightly damped, so that the sensor is most sensitive to vibrational frequencies within a few kilohertz of its resonant frequency, and becomes less sensitive rapidly to vibrational frequencies much higher than the resonant frequency. One such high-frequency vibration sensor is Vibrametrics (V 1bra-Mc
trics, Inc.) product name VM1018
It is an accelerometer. 1. During a crop size inspection operation, the tool holder and cutting insert 18 (FIG. 1) are moved rapidly toward the workpiece 14 at a rate of approximately 1 inch per minute until contact occurs. to slow down. Continuous traverse noise is sensed, which is the background noise generated by normal operation of the machine tool when the tool and workpiece are not in contact. Some machine tools may produce short-duration, high-amplitude spike-like noises, while others are relatively quiet and do not produce such noise pulses. When the slowly advancing tool insert first contacts the workpiece, there is a sudden and nearly continuous increase in vibration level. These vibrations are detected by an accelerometer and converted into electrical signals.

The high-pass vibration signal is filtered by a wave filter 37 .

The cutoff frequency of this wavelet is slightly lower than the sensor's resonant frequency to discriminate high amplitude mechanical noise that tends to be concentrated at relatively low frequencies. The combination of a resonant accelerometer and a bandpass-wave device produces a band-wave effect on vibration signals having frequencies within a band of about 20 KH2 around the accelerometer's resonant frequency. High pass-
The rectifier is used to boost the weak tool contact signal from the sensor to the level required by the subsequent rectifier stage of the machine.
It has a high gain of about 60 or 70db.

The combination of a double-wave rectifier and a low-pass waveform detector acts as a double-wave energy detector 38 (the single-wave action is too strong for true envelope detection), converting the bipolar sensor signal into a single-polar "envelope" signal. ” into a signal.

The cutoff frequency of a low pass filter is typically 500
Hz, which prevents aliasing from subsequent sampling operations as long as the sampling frequency is sufficiently higher than the Nyquist frequency of 1KH2.

Thus, the sampling period can be long enough to perform the necessary digital analysis of the signal between samples of the analog signal. In fact, the cutoff frequency of a low pass filter can be as low as 100H2. The unipolar signal at the output of the analog preprocessor is the third
As shown in the figure. A low continuous traverse noise signal is shown at 39, and a large amplitude noise spike is shown at 40.
, and a gradually increasing tool contact signal is shown at 41. As previously mentioned, some lathes and machine tools have pre-contact vibration signals that do not have such noise spikes.

A signal sample extracted by the sampler 42 from the output from analog signal processing is converted into a digital format by an analog-to-digital converter 'a43, and then sent to a digital circuit 44.
further processed and analyzed by. The digital circuit 44 can be a programmable general-purpose implementation. The digital circuitry recognizes signal patterns associated with tool contact events and, when predetermined contact detection criteria are met,
Generates a contact alarm signal. This signal is sent to the control 45 of the machine tool, which stops the advance of the tool and measures its travel from the starting reference position to the surface of the workpiece. A part size calculator and display 46 converts this information into part dimensions and displays the results.

Tool contact detection devices ignore noise spikes, even if they are present, and issue an alarm several milliseconds after the tool first contacts the workpiece. False alarms, such as those caused by noise spikes, are prevented.

FIG. 4 illustrates one method for enabling a tool contact detection device to eliminate noise spikes while detecting tool contact signals, namely 'tril) and tool contact confirmation detection methods. are doing. Select and preset an amplitude threshold level 47, which is a minimum multiple of the peak of the continuous traverse noise signal generated by machine tool operation without tool-workpiece contact, e.g. Place it in a place that is twice or three times higher. If desired, the amplitude threshold level can be made to follow changes in the noise level of the machine tool operation. When the noise spike 40 crosses the amplitude threshold, it is detected and trips the detector. The algorithm enters a verification period that is set slightly longer than the maximum known duration of the noise pulse. During this verification period, the algorithm continuously examines signal samples above the amplitude threshold. If fewer than a preset number N of such samples are detected during the verification period, the noise pulse is rejected or discarded as a false touch signal. When the signal rises above the amplitude threshold 47 due to rubbing contact between the tool and workpiece, the algorithm again enters the verification period. In this case, the signal samples are above the amplitude threshold 47 for the entire verification period, and before the verification period expires, the number of samples above the amplitude threshold is set to the preset It
! When N is reached, a tool contact event is generated. Alternatively, a 4 non-pull lower than the amplitude threshold can be used. In this case, the detection logic is reversed. Generate an alarm if N samples are not counted during the verification period.

In this case it is a preset number of samples below the amplitude threshold.

Figures 5a and 5b show another method of detecting tool contact using an increment/subtractor vlB, which allows the tool contact detection device to ignore the I-sound spike while detecting the tool contact signal. is exemplified. Digital circuit 44
The increment/decrement counter, which forms part of
The tool contact alarm threshold is set in advance, and whenever the amplitude of the signal sample exceeds the amplitude threshold, the count is increased toward the alarm threshold, and when the amplitude of the signal sample is smaller than the amplitude threshold, the alarm threshold is always set. Count down in the opposite direction from . Alternatively, the counter may count down on samples above the amplitude threshold and count up on samples below the amplitude threshold. In this case, the alarm threshold can be set to count O.

The alarm threshold is set to be greater than the number of signal samples that can occur during the longest expected noise spike duration, so that a 1 m noise spike will not cause an alarm. determined. For example, in Figure 5b, the alarm threshold count TA is count 4 (in reality, this is a much larger count). At the times of the second to fifth samples after the first detection of a sample higher than the amplitude threshold, two samples higher than the amplitude threshold value increment the word counter, and samples smaller than the amplitude threshold value increment the word counter. is subtracted and returns to O. This will cause the noise spike to be ignored and no alarm will be raised. A valid tool contact signal 41 is @width14 throughout the verification period.
Generate samples higher than the value. In this case, as each sample is detected and analyzed, the counter is incremented and a contact alarm is generated at count 4. Tool contact signal is TA
remains high for a period of more than T samples, generating a tool contact alarm at the T^th signal sample after the contact signal first exceeds the amplitude threshold.

The subtraction rate can be set to be greater than the increment count rate to avoid alarms caused by closely spaced noise spikes.

FIG. 6a shows a flowchart and tool contact signal pattern recognition logic for implementing the trip and contact confirmation detection method shown in FIG. 4 using samples above the amplitude dark value. The digital circuit 44 has a programmed meter OH
may have two counters, both of which are O
In contrast to the counter shown in Figure 5b, which counts up starting from 0, it counts down to O. Counter B counts all signal samples starting from the first sample above the amplitude value and is reset when it decrements to zero. This counter determines the confirmation period. Counter A is the amplitude amount pi (
It is a higher signal sample.
It is reset when the number is decreased to . An alarm is generated when counter A decrements to O.

In the first step 49 after "r start", the operator sets the amplitude to 1;
Set 211Q = T. The amplitude threshold is actually the third
This is a predetermined number of counts in the Δ/D converter 43 in the figure, and one count represents approximately 2.5 millivolts. In the next steps 50 and 51, the counter AtfiN is set and the counter B is set to M. ) where M is greater than or equal to N (M and N are entered by the operator in step 49). In this example, to simplify the explanation of the operation of the logic, both N and M are assumed to be 3 counts, but the actual counting period of the ramble used and the duration of the noise spike that actually occurs are N is normally set to about 15, and M to about 20.

Referring to FIGS. 6a to 6C, initially the counter A counts N=3. The π1 counter A, which counts all signal samples above the amplitude threshold in step 52, is determined to be N, and therefore, in step 53, sample 1
Inspect. Step 54 calls for comparing the amplitude of the sample to an amplitude threshold. In this case, since sample 1 is below the amplitude threshold, nothing happens and the next lean pull is tested via logic loop (2). Note that logic loop ■ is followed when the signal is less than the amplitude threshold, and none of the word counters change. Signal sample 2
, the noise spike signal is higher than the amplitude threshold and counter A has N=3 counts. Steps 52 to 54
After applying ★, it passes through the logical loop ■, and steps 55 and 56
requires both counters A and 8 to be reduced to 2. If one sample higher than the amplitude threshold is detected, do not follow logic loops ■ and ■. In signal sample 3,
The noise spike signal is higher than the threshold, and this clock counter A is 2
count (not equal to N count). Step 52
The process then branches to step 57, where the next sample is tested, and the process proceeds to steps 58-61. Since the sample is above the amplitude threshold, we decrement the counter A and then test whether the counter A=0 (in this case, A=not 0).
Decrement counter B. For this reason, both counters are reduced to 1 via logic loop 2. Step 62 is counter B=0
Check whether it is. In this case, it is not B-0, so steps 52 and 57 test the next sample. At signal sample 4, the noise spike ends, so the signal is less than the amplitude threshold. At step 58, a branch is made to logic loop 2, where only counter B is decremented. Since this counter B reaches 0, step 62 instructs steps 50 and 51 to reset both counters to 3.

At signal sample 5, the touch signal begins and the signal becomes higher than the width threshold. Both counters A and B are reduced to 2 via logic loop ■. At signal sample 6, the touch signal continues to rise, so that a sample above the amplitude threshold is detected. Since counter A is 2 (not equal to N), both counters are then reduced to 1 via logic loop ■.

At signal sample 7, the touch signal continues to rise so that the signal is above the amplitude threshold. Counter A is decremented to 0 in step 59 and branches to step 63 in step 60 where a touch detection alarm is generated. This is the end of the program.

In summary, if both counters are above the amplitude threshold,
Start by sample. Counter B that determines the confirmation period
counts the next M samples before resetting itself and counter A. When counter A is set to count samples higher than the subsequent amplitude threshold, if counter A counts the number of samples of IW before counter A is reset by counter B, the tool contact information An alarm indicating that Otherwise, both counters are reset until another verification period of M counts of counter B is initiated by another sample above the amplitude threshold.

As an alternative, counter A can be set to count subsequent samples below amplitude ra+i, as shown in FIGS. 7a-17c. Counter AIf
If counter B reaches O before counting iNIIN samples, an alarm representing tool contact information is generated. When counter A counts N samples, both counters and B are reset. In the example of FIGS. 7a and 7c illustrating this alternative scheme, M=6 and N=3. Process 6
4 to 66 are the same as the first method. Steps 67 and 6
At 8, sample 1 is tested and is below the amplitude threshold, so
The next sample is tested. Since sample 2 is above the amplitude threshold, counter B is decremented by steps 69-71. At this time, counter B is not O, so sample 3
is inspected. Since this sample is not below the amplitude threshold (step 72), counter B is decremented again. Following the logic loop, steps 72-74 cause counter A to be decremented since signal sample 4 is below the amplitude threshold, and since counter A is not zero, counter B is decremented again. Samples 5-7 are all above the amplitude threshold and counter B is decremented repeatedly until B=O.

When B=O, the process branches to step 70 and a contact alarm is generated (step 75).

If there are no samples below the amplitude threshold, as in the case of a quiet machine tool, after a predetermined number of counts, counter B goes directly to zero and an alarm is generated. Note that the noise spike is immediately rejected when a sample below a predetermined number of amplitude thresholds is detected.

FIG. 8a is a flowchart 1- for implementing the increment/decrement counter method shown in FIGS. 5a and 5b, and shows tool contact signal pattern recognition logic. This method increments if the sample is below the amplitude threshold;
One counter is used that counts down if the sample is above the amplitude threshold.

When the counter decrements to O, the device issues an alarm.

The first step 76-78 after "Start" is for the operator to set the retention width threshold = King, the counter = N, and the sample to be inspected. In this example, N=3 to simplify the explanation. Signal sample 1 is below the amplitude threshold and the counter is N
is set to . At this time, the logic loop (2) including steps 79 and 80 is followed to test the next sample. Signal sample 2 is a noise spike signal and the counter is still N
It is. Then, by logic loop ① and steps 81 and 82, the counter is reduced to 2, but not O, so the next sample is tested. Signal sample 3 due to the noise spike is above the amplitude threshold and the same logic loop reduces the counter to one. Signal sample 4 is below the amplitude threshold because the noise pulse has ended. Therefore, in step 80,
Branching to logic loop 2, step 83 increments the counter to two.

Signal sample 5 is at the beginning of the touch signal and is above the amplitude threshold. The logic loop ■ decrements the counter to one.

A signal sample 6 from the rising touch signal is taken (until above the amplitude threshold).

In steps 81 and 82, the counter is decremented to O, and step 84
branch, and a contact alert is generated. This is the end of the program. Before an alarm can be issued,
The number of samples above the amplitude threshold must exceed the number of samples below the amplitude threshold by a predetermined number. If the lathe or other machine tool to be monitored has a relatively quiet operating mechanism and does not generate noise spikes whose amplitude exceeds the set amplitude threshold, then FIG.
The tool contact signal pattern recognition logic shown in FIGS. 7a or 8a follows a normal routine to detect a gradually increasing contact tool signal and generate a valid alarm. In FIG. 6a, the logic loop ■ is followed until the signal sample exceeds the amplitude threshold. The first sample above the amplitude threshold causes both counters to be decremented by the logic loop ■. Subsequent samples are above the amplitude threshold and counter A is not N (so the logic loops until a training alarm is generated)
I passed through several times. Figure 7a was discussed above.

Referring to FIG. 8a, when a sample is below the amplitude equivalence, logic loop 2 is passed through until a sample above the amplitude equivalence is detected. Thereafter, the logic loop ■ is passed through several times until an alarm is generated.

This vibration sensing tool contact detection device is useful as a stand-alone device, and can also be used in numerically controlled machine tools. The advantages of using cutting tools as probes for on-line inspection of workpiece dimensions have been previously discussed. Another advantage of this contact detector and method is that it can be easily combined with an acoustic single tool breakage detector into a tool contact and tool breakage detection system.

Although the invention has been illustrated and described with reference to preferred embodiments, it will be appreciated that many modifications can be made within the scope of the invention by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a partial side view of a horizontal turret lathe showing alternating positions of the accelerometers. FIG. 2 is a simplified side view of a vertical turret lathe showing alternating sensor locations. FIG. 3 is a block diagram of the tool contact detection device. FIG. 4 is a graph showing a vibration signal output by analog signal processing to illustrate the trip and contact confirmation detection method when spike noise is present. Figures 5a and 5b are extra ¥! 2 is a graph showing vibration signals and increment/counter counts in connection with the i/decrement counter contact detection method; Figure 6a shows 1 using samples higher than the amplitude equivalence.
FIG. 3 is a flowchart of a program for the second (tripping and confirmation) method; FIG. Figure 6b is a graph showing the counts of B to the counter. FIG. 6C is a graph showing noise spikes and touch signals at several sample times. Figure 7a is a 70-chart of another method using samples below the threshold. Figures 7b and 7c are graphs showing the counter counts, noise and touch signals, respectively, for the case of Figure 7a. FIG. 8a is a program flowchart for the second (increment/decrement counter) method. Figure @8b is a graph showing the count to valid alarm. FIG. 8C is a graph showing noise spikes and touch signals at several sample times. 11: Spindle 12.25: Chuck 13.26: Jig 14.27: Workpiece 16.30: Tool turret 17.31: Tool column 18.32: Tool holder and cutting insert 21.23.3
3.35: Vibration sensor 19: Turret stand

Claims (1)

[Claims] 1) In a device for acoustically detecting the initial contact of a cutting tool with a workpiece in a machine tool, a vibration sensor having the highest sensitivity to frequencies centered around the resonance frequency, a vibration sensor located on the machine tool to sense vibrations at the interface of the workpiece and converting these vibrations as well as other vibrations into electrical signals and to discriminate noise at lower vibration frequencies of the machine; an analog device comprising means for high-pass filtering and amplifying said vibration signal, and means for rectifying and low-pass filtering said signal to detect energy in a band centered on said resonant frequency. a preprocessing device; means for sampling the unipolar signal at the output of the preprocessing device and converting each sample into digital form; means for comparing each sample with a known amplitude threshold level that is a predetermined minimum multiple higher than a continuous noise level that
a digital circuit having means for generating a contact alarm signal immediately after one sample is detected, the contact alarm signal being sent to a control of the machine tool for stopping advancement of the cutting tool; equipment with 2) The apparatus of claim 1, wherein the vibration sensor is a high frequency accelerometer with a resonant frequency higher than 40 KHz. 3) In the apparatus according to claim 1, the cut-off frequency of the low-pass filter is lower than 500 Hz, and the sampling frequency of the sampling means is higher than 1 KHz to prevent aliasing. A device that is the sampling frequency. 4) The apparatus according to claim 1, wherein the digital circuit verifies tool contact after detecting one sample above an amplitude threshold to prevent false alarms, and Apparatus including means for ignoring spike-like noise pulses prior to contact. 5) In a tool contact monitoring device that detects contact between a cutting tool insert and a workpiece in a machine tool, electrical signals representing vibrations at the interface between the insert and the workpiece as well as other machine tool noises are used. a broadband vibration sensor for generating a signal; means for high-pass filtering and amplifying said vibration signal to discriminate against machine noise with lower vibration frequencies; and means for rectifying and low-pass filtering said signal. means for sampling the unipolar output signal of the analog processing means and converting each sample to digital form; examining every signal sample; means for detecting when the amplitude of the signal is greater than an amplitude threshold level set at a continuous traversal noise signal level multiplied by a minimum multiple, and remains above said amplitude threshold for a predetermined verification period; means for detecting a valid contact confidence that is, and rejecting spike-like noise pulses higher than said amplitude threshold as false contact alarms, and generating a contact alarm signal to be used to stop advancement of said tool insert; and a digital pattern recognition circuit comprising means for monitoring tool contact. 6) A tool contact monitoring device according to claim 5, wherein said means for rejecting noise pulses and detecting tool contact signals counts samples higher than said amplitude threshold during said verification period. , a tool contact monitoring device comprising counting means for rejecting when a preset number of samples higher than the amplitude threshold are not detected during the verification period. 7) In the tool contact monitoring device according to claim 6, the counting means is composed of two counters, one counter counts all the samples, and the other counter counts all the samples. A tool contact monitor that only counts samples above an amplitude threshold. 8) A tool contact monitoring device according to claim 5, wherein said means for rejecting noise pulses and detecting tool contact signals counts samples lower than said amplitude threshold during said verification period. , means for rejecting a spike-like noise pulse when a predetermined number of samples below the amplitude threshold are detected during the verification period. 9) In the tool contact monitoring device as set forth in claim 5, the means for rejecting noise pulses and detecting tool contact signals increments with samples higher than the amplitude threshold; an increment/decrease count that performs subtraction counting on samples below a threshold, or vice versa, and issues an alarm when the number of samples above the amplitude threshold exceeds the number of samples below the amplitude threshold by a predetermined number; A tool contact monitoring device consisting of a 10) In the tool contact monitoring device according to claim 5, the vibration sensor is a high frequency accelerometer,
A tool contact monitoring system, wherein said energy detection means comprises a rectifier and a low pass filter having a cut-off frequency lower than 500 Hz, and wherein the signal sampling rate of said sampling means provides anti-aliasing filtering. 11) In a method for detecting the initial contact of a cutting tool insert with a workpiece in a machine tool, when the tool insert slowly advances toward the workpiece and makes rubbing contact, It senses vibrations, converts them into electrical signals, amplifies and band-pass filters them to discriminate against mechanical noise with lower vibration frequencies, and then rectifies and low-pass filters the energy in the band. pre-processing the vibration signal by detecting, the output signal of this processing including an indication of a tool contact event, a high amplitude noise spike generated by a mechanism of the machine tool, and a continuous traverse noise; sampling the output signal and converting each sample to digital form; testing every signal sample against an amplitude detection threshold greater than a continuous traverse noise signal level of the machine tool; and testing every signal sample above the threshold; detecting the noise pulse, and then examining one of the samples above the threshold and the samples below the threshold for a period longer than the maximum known duration of a large amplitude spike-like noise pulse; ignoring as an alarm and generating a tool contact alarm when samples higher than the threshold are detected throughout the period. 12) In the method described in claim 11,
The amplitude detection threshold is preset and is approximately two to three times the signal peak of the continuous traverse noise signal. 13) In the method described in claim 12,
Samples above the threshold and samples below the threshold are counted in a first counter, only samples above the threshold are counted in a second counter, and the first counter Both counters are reset after counting samples, and the second counter generates the contact alarm after counting a preset number of samples above the threshold before the end of the period. 14) In the method described in claim 12,
The method in which samples below the threshold are counted and the alarm is generated when a preset number is not counted before the end of the period. 15) In the method described in claim 11,
The contact alarm is generated immediately after counting a preset number of samples higher than the threshold if no noise spikes of high amplitude are generated by the mechanism of the machine tool.